Sound in buildings is as designed as light, even when it doesn't feel like it. Reverberation time (RT60 — how long a sound takes to decay 60dB) shapes how a space feels and functions.

A cathedral at 8–10 seconds RT60: each sound hangs in the air, layers with the next, produces the "holy" wash. A recording studio at <0.3s RT60: dead, analytical, no room sound. A good concert hall at 1.5–2s: warm, enveloping, the orchestra sounds larger than it is.

Building materials determine RT60. Concrete reflects; fabric, wood, and irregular surfaces absorb. Modern glass-and-steel buildings often have too-long reverb, making speech intelligible only at close range.

Related: [[city-as-hypertext]], [[thermal-mass-passive-design]]